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She later suffered a massive hypoglycaemia-related cerebral injury and died on January 2, 2013.

It became clear after an investigation that her death had been a result of higher levels of insulin in her body.

A coroner's inquest before chief coroner Judge Deborah Marshall is being held over the next two weeks in the Auckland District Court to determine the source of the insulin.

Police have not ruled out reinvestigating her death based on the findings of the inquest. The case remains open.

Dr Isuru Seneviratne, one of two ICU registrars at Middlemore that night, said in a witness statement to police on December 31 that he was called to an emergency in the burns unit at 1.45am on December 27.

There was already a team caring for Bills when he arrived, the medical registrar, medical house officer, night house officer of the burns unit, the patient at risk (PAR) team, and a nurse.

"Walking into the room, what I remember is that Heather looked like she was working quite hard to breathe. She had the oxygen mask on. She had her eyes open and appeared to be alert but was not speaking or anything like that," he told police.

"I was aware of Heather's background as I had seen her before a few times in ICU."

Seneviratne said he asked for a blood sugar level and was told it was normal.

"I cannot remember who told me this as I was receiving quite a lot of information at the time from the people who were working with Heather prior to me arriving.

"I personally did not see the finger prick for the blood sugar level test being done. I cannot remember the exact words I was told, whether it was a figure or if I was simply told it was normal or okay."

The doctor didn't see that blood sugar was an issue and concentrated on trying to improve Bills' blood oxygen levels.

"At this point I asked to get an arterial blood gas (ABG) done but was told by the house officer it had already been done. He verbally gave me the figures," he said.

The ABG was performed at 1.46pm, he said, before he arrived.

"I'm not sure who did the ABG, I assume it was the night house officer for the burns unit."

Heather Bills was rescued from her burning home but died in hospital. Photo / Michael Craig

A chest X-ray was taken to help address the breathing issues, and Seneviratne consulted with Dr Tony Williams with a decision made to transfer Bills to ICU.

But when Seneviratne returned to see Bills after checking the ABG results he found she had deteriorated further, he said.

"I decided we would need to intubate her, or in other words place a tube in her windpipe to assist her breathing.

"The PAR nurses noticed Bills drooling and appeared to have some facial droop. It was suspected she may have had a stroke."

Bills' eyes were no longer open and at one stage she stopped breathing altogether, he said.

A CT scan was then performed.

"Then after looking at the notes [I] saw that the blood sugar level was 0.1 on the ABG test," Seneviratne told police.

"I was a bit confused because I was not expecting to see that and then I looked at the first one and saw that was 1.8 and then it dawned on me that Heather's situation could all be related to the blood sugar."

He asked the nursing staff to give Bills a blood sugar level test, which confirmed her levels were low, he said.

The critically ill patient was then given "quite a big dose" of glucose solution to boost her sugar level.

"My initial thought from an end-of-bed inspection was that Heather was in respiratory distress and looked fluid overloaded," Ching said.

Toor struggled to feel a radial pulse and a chest X-ray was performed.

Ching said she did not note any insulin on Bills' chart.

The ICU team and PAR team were then called to take over.

"I do not recall seeing syringes or any medications in Mrs Bills' room on the initial review prior to the [emergency team] arrival," Ching said.

She provided her notes to police on February 28, 2013.

Later she agreed with a medical expert that hypoglycaemia should be considered as the cause of a Bills' collapse.

WHERE TO GET HELP:

If you are worried about your or someone else's mental health, the best place to get help is your GP or local mental health provider. However, if you or someone else is in danger or endangering others, call police immediately on 111.